CAIRO — Thousands of Egyptians, increasingly impatient with their interim military rulers, rallied Friday in the nation's two largest cities, ringing a security building with chants of "Oh police, you are thugs" and demanding trials for police officers suspected of killing of hundreds of activists in the uprising that brought down Hosni Mubarak.

The protests in the capital of Cairo and the port city of Alexandria were billed as the "Friday of Last Warning" to the military council that took over from Mubarak and is to lead Egypt to democracy. Large crowds streamed into Cairo's Tahrir Square as the sun set, bringing relief from the day's soaring temperatures.

The Muslim Brotherhood, Egypt's best-organized political group, and the ultra-conservative Salafi movement stayed away. The Islamists are campaigning hard for upcoming parliamentary elections later this year and apparently want to avoid friction with the military rulers whose decisions will set the final date and rules for the vote.

For the past week, hundreds of hardcore activists have camped out at Tahrir Square, birthplace of the 18-day popular uprising that ousted Mubarak on Feb. 11. Their main demand is that the military council purge all remnants of the Mubarak regime.

"We want to cleanse the country's institutions," one of the demonstrators, standing on a stage in a corner of the square and holding a microphone, told a group nearby. "Until we see the government officials (talking to protesters) in Tahrir, we will not leave this place."

"Bread, freedom and social justice," he chanted.

The protesters' frustration was reflected in new graffiti on the wall of Cairo's biggest government building which faces the square. "The revolution has protectors," read one slogan, referring to the protesters' determination to keep going until their demands are met. A second depicted the military council as hand holding a hammer crushing the "Egyptian will."

Another new drawing reflected widespread skepticism that Mubarak will be punished. The graffiti showed Mubarak dangling from a rope, with the caption: "Message from the military council: don't believe this drawing."

Mubarak will be tried on August 3, over the killings of protesters and corruption charges. In a transcript of his interrogation published by two newspapers Thursday, the 83-year-old Mubarak denied any responsibility for the killing of nearly 900 protesters by his security forces. Mubarak, Egypt's president for three decades, is in custody in an Egyptian hospital.

"The revolution is not complete yet," said demonstrator Wael Malak, who temporarily closed his shop in the Egyptian Red Sea resort of Sharm el-Sheik because the political turmoil in Egypt led to a sharp drop in tourism. Malak complained of a lack of security in post-uprising Egypt.

A second protester, Salim Youssef, said the military only responds to public pressure and that marches must therefore continue.

Though Friday's crowd was smaller than usual, the number of tents and those camping in Tahrir Square increased since earlier in the week. Coils of barbed wire were added to makeshift security checkpoints set up at the entrances to the square. The checkpoints, staffed by volunteers, are meant to deter sudden attacks from assailants or a police crackdown.

In Alexandria, thousands of protesters rallied outside the local security headquarters, chanting: "O police you are thugs."

Some jumped over a high fence surrounding the building, the local branch of the Interior Ministry, tore down the police flag and replaced it with the Egyptian flag. They sprayed anti-police graffiti on the walls and covered the ministry's golden emblem with the words "The Ministry of Torture."

Several protesters tried to storm the building, but others prevented them while chanting "peaceful, peaceful."

Activists distributed leaflets listing names of police officers believed to have been involved in killings and torture of protesters. One of the protest groups, known as April 6, said a notorious police commander in Alexandria, known as the "flogger of the activists," had been promoted to a top security position in the city.

Security forces stayed away from Friday's protests.

Earlier this week, Egypt's security chief dismissed hundreds of high-ranking members of the security forces, including those charged in the killing of protesters.

Meanwhile, the semi-official Al-Ahram newspaper reported that Egypt's former prime minister, Atef Obeid, was detained for 15 days on suspicion of corruption and permitting the sale of a nature reserve in the ancient city of Luxor to a Mubarak associate, business mogul Hussein Salem.

Egypt has demanded Salem's extradition from Spain. The mogul is wanted for trial on corruption charges, mostly arising from his alleged use of Mubarak's name to buy state land cheaply.

Obeid was prime minister from 1999 to 2004.

His deputy and former minister of agriculture, Youssef Wali, was also detained for 15 days for permitting the import of potentially cancer-causing pesticides.

Obeid and Wali were taken to Cairo's Tora prison, where a string of former top regime figures — including another former prime minister, ruling party chief and chief of staff — are already languishing, facing similar corruption investigations.